The hair dye component, HC Blue 1 was subjected to HPLC to isolate impurities that may be responsible for its mutagenicity. The commercial dye and its mutagenic fraction, but not the HPLC-purified dye, produce DNA adducts in Salmonella. These results show that the mutagenicity of HC Blue 1 due to its impurities. The food mutagens, IQ and MeIQ, were studied following activation by S9 from different rat strains in the presence of biogenic amines. Tryptamine enhanced IQ mutagenicity by Fischer rat S9 and inhibited it with Sprague- Dawley and Wistar rat S9. Tryptamine enhanced the mutagenicity of MeIQ, regardless of the S9 source. Tyramine produced different patterns, and histamine had no effect. These patterns of interactions suggest rat strain differences in the activation of IQ and MeIQ. Preincubation of Salmonella and metal salts in distilled-deionized water resulted in the detection of mutagenic activity with cobalt chloride, ferrous sulphate, cadmium chloride, and zinc chloride; phosphate buffer, which is normally used, reduces or eliminates the mutagenicity. Magnesium and citrate in the minimal medium were also responsible for these effects. HEPES buffer does not inhibit mutagenicity and may be a good alternative to phosphate for use with bacterial and mammalian cells.